Thermoplastic materials, such as PET (polyethylene terephthalate), have been used for some time now to make containers. This is particularly true for food-containing containers, especially drinks. Although said containers can be of different types, they shall be referred to hereinafter generically as bottles, which happen to be the most popular.
One of the main problems encountered when thermoplastic materials such as PET are used for making bottles is that the necessarily thin and inherently somewhat microporous wall of the formed material make the bottle walls permeable to gas. The result is that oxygen can permeate into the bottle from the outside environment possibly altering the contents of the bottle through oxidation, and carbon dioxide found in carbonated drinks can seep out of the bottle possibly negatively affecting the taste characteristics of the product and damaging the image of the drink manufacturer.
Furthermore, bottles may suffer from impacts during transport, handling, and warehousing leading to visible damage to their outer surface.
To resolve these inconveniences, containers, especially bottles, can be protected with a thin, clear coating that is not very permeable to gas; is able to resist impacts and abrasions if possible; and does not affect the overall appearance of the product.
For example, U.S. Pat. No. 5,658,619 describes a process for coating bottles. This process involves sending bottles to a coating segment where the bottles are gripped and dipped one at a time in one of many containers filled with a coating solution consisting of a resin dispersed in a solvent. Then, after removing the bottles from the coating solution, the bottles are released and sent to a flash-off segment where the solvent of the coating solution is removed from the coating applied to the outer surface of the bottle. After the flash-off process, the bottles are sent to a curing station where the resin of the coating is cured.
Such a plant is complex and not easy to run, particularly when it comes to transferring the bottles from one treatment segment to the next since each segment uses a specific bottle-handling device. Furthermore, this plant requires long drying times, meaning that the time the bottles stay in the drying furnace is very long. The conceivable solution of increasing the drying temperature is not viable due to the low softening point of the thermostatic material used to make the bottle; obviously, this solution could result in deformations to the bottle.
Today, thus, no paint-drying process exists that is simple, effective, and fast; in addition, no relating plant exists that is compact and effective.